any medium bore paintballs. get a paintball, put it in...it should not roll through immediately. blow on it and it should fly out easily. if it gets stuck it's too big, if it rolls through it's too small. diablo dusk is a bit too small for this barrel.

Strengths:

it's cheap, made of strong aluminium, accurate

Weaknesses:

its kind of ugly looking

Review:

This is the first barrel I bought for my Spyder after being tired of the stock barrel. I was really pleased with the accuracy increase for the price(about 40 dollars). Friends of mine who tried it out also liked it. I tried out a friends night stick and did not see any visible increase in accuracy. the paint to bore match is really important, so make sure you test your paint with your barrel. I like this barrel, it is quite cheap, and it's made out of aluminum which is very strong.

Conclusion:

This is a good barrel for a cheap price. I was new to the sport and thought this was the cheapest you could get, but I noticed now you can get the J&J Ceramic for only about $35. Try that too.